Methods for printing of three-dimensional objects

ABSTRACT

A method to help control the quality of printed three-dimensional objects is provided. The method may include printing a carpet of building material on a printing tray below and/or around the base of an object prior to printing the object such that the carpet may include one or more layers of modeling material. According to embodiments of the invention the carpet is served to prevent infiltration of air and/or radiation between the base of the object and the tray to prevent detachment of the object from the tray.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application of U.S. patent applicationSer. No. 10/537,458, filed Jun. 3, 2005, which is a National PhaseApplication of PCT International Application No. PCT/IL2003/001024,International Filing Date Dec. 3, 2003, entitled “PROCESS OF ANDAPPARATUS FOR THREE-DIMENSIONAL PRINTING”, which in turn claims priorityfrom U.S. Provisional Patent Application, 60/430,362, filed Dec. 3,2002, which are all incorporated by reference herein in their entirety

FIELD OF THE INVENTION

The present invention relates to apparatuses and methods useful inthree-dimensional object printing. Specifically, embodiments of thepresent invention relate to systems, methods, and apparatuses forhelping to improve the quality of printed three-dimensional objects.

BACKGROUND OF THE INVENTION

Three-dimensional (3D) printing is a process used for the printing ofthree-dimensional objects, for example by printing or building parts ofsuch objects in layers. Such 3D objects may be used, for example, forprototype parts.

Various systems have been developed for three-dimensional printing,wherein material for object printing is deposited in consecutive layersaccording to a pre-determined configuration or in selected arrays asdefined by, for example, a Computer Aided, Design (CAD) system connectedto the printing systems. Such materials may include materials forconstructing an object and materials used for constructing supportstructures for an object.

According to some apparatuses, systems and methods for 3-D printing,predetermined or preprogrammed configurations and designs using, forexample, CAD software, may aim at obtaining as accurate a final productas possible. However, each printed product or model is different,whether in shape, design, size, bulk, composition and so on, and thesedifferences may be affected by different factors during the printingprocess, such as heat, chemical reactions of the photopolymer materialto curing, internal strains (e.g., within the object) due to strainssuch as, for example shrinkage of the materials during curing and/orcooling, environmental influences within the printing apparatus, forexample temperature fluctuations etc. Adverse effects may take ondifferent forms such as various deformations in the finished product. Inaddition, the quality of the finished product may be affected by theseand other factors.

SUMMARY

Embodiments of the present invention provide apparatuses and methods forcontrolling the quality of printing in three-dimensional object-printingsystems. A printing system, according to some embodiments of the presentinvention, may include a printing apparatus to print three-dimensionalobjects; a controller that may prepare the digital data thatcharacterizes the 3-D object for printing, and control the operation ofthe printing apparatus; and a printing tray with a selected adhesioncharacteristic. The adhesion characteristic may be, for example, a highadhesion coating for high adhesion to the object's building material(s).The surface coating of the tray may be, for example, an anodizedaluminum coating, which may include, for example, pores containing amaterial that acts to adhere to the printed objects. The pores may, forexample, be filled with water. Alternatively, the printing tray may bepretreated with water.

According to some embodiments of the present invention the printingsystem may include a printing apparatus to print three-dimensionalobjects; a controller programmed to control the printing apparatus; anda printing tray with a thermal expansion coefficient similar to that ofan object to be built. The printing tray may include organic materialand/or may include material whose thermal expansion coefficient may besubstantially similar to that of the objects being printed.

According to some embodiments of the present invention, a printingapparatus for three-dimensional printing may be provided that mayinclude a printing head (e.g., an ink jet head or another suitablematerial deposit system or dispenser) to deposit material for athree-dimensional object; a printing tray to support the objects beingprinted by the apparatus; and a temperature control unit to control thetemperature in the apparatus. The temperature control unit may include,for example, a heating source or mechanism and a cooling source ormechanism. The temperature control unit may be integrated into theprinting tray. For example, the printing tray may include coolingtunnels and/or heating elements and/or temperature sensors.

According to some embodiments of the present invention a printingapparatus for three-dimensional printing may include a printing head, aprinting tray, and a blowing unit to cool layers of an object afterprinting. In other embodiments such a printing apparatus may include asucking unit to cool layers of an object after printing.

According to some embodiments of the present invention the printingapparatus for three-dimensional printing may include a printingsub-system or other suitable container which may be insulated for, forexample, temperature control. The cell may include a temperature controlunit. The temperature control unit may include a heating source ormechanism and/or a cooling source or mechanism. Heating of the cell, forexample, may be brought about by the tray, which may be heated byheating elements. The printing sub-system may include material that maybe reflective in the IR wavelength region. The printing sub-system mayinclude at least one insulation structure. The printing sub-system mayinclude an upper heating element, radiation source, lamp, or othersuitable heat source, to control the temperature of the printingsub-system and/or heat the upper layers of an object being printed.

According to some embodiments of the present invention, the printingapparatus may include a printing sub-system and an insulation area toinsulate an object or set of objects whose printing may be complete. Theinsulation area may include a temperature control unit. The printingapparatus may include at least two printing trays.

According to some embodiments of the present invention athree-dimensional printing system may include a printing nozzle detectormechanism. Nozzle status data detected by the nozzle detector mechanismmay be computed and/or analyzed by a controller, for example, usingsuitable executable code.

According to some embodiments of the present invention the printingsystem may include one or more leveling devices associated with aprinting head array.

According to some embodiments of the present invention the printingsystem may include a curing lamp located at a side of the printing head,and a leveling device and/or another curing lamp located at the otherside of the printing head.

According to some embodiments of the present invention a printingapparatus for three-dimensional printing may include a controller tocontrol construction of building material at the base of an object to beprinted, and print the object on the construction. The controller mayact to dispense building material beneath the base of said object to beprinted. The construction may adhere to the object and to a printingtray on which the object is to be printed. The construction may providea barrier layer between the object and the printing tray. Theconstruction may provide a carpet between the object and the printingtray. The construction may provide a pedestal between the object and theprinting tray. The construction may raise the object being built withinthe leveling range of a leveling device.

According to some embodiments of the present invention a printingapparatus for three-dimensional printing may include a controller tocontrol the building of a thickening layer of building material of apredetermined thickness around a printed object. The thickening layerinclude one or more building materials.

According to some embodiments of the present invention a printingapparatus for three-dimensional printing may include a controller toposition a printing tray at a relatively high level prior to printing,the level enabling compensation for shrinkage in a previously printedand cured layer.

According to some embodiments of the present invention a printingapparatus for three-dimensional printing may include a controller tocontrol the delivery of shockwaves to a printing tray holding a printedobject.

According to some embodiments of the present invention a printingapparatus for three-dimensional printing may include a controller tocontrol the printing of a three-dimensional object with an adjacentsupport construction, the object and the support construction beingseparated by a barrier, the barrier including vacant pixels.

According to some embodiments of the present invention a printingapparatus for three-dimensional printing may include a controller tocontrol the printing of a support construction, the support constructingincluding support material and modeling material elements within thesupport material, the modeling material elements being used to reinforcethe support material. The support construction may include a grid ofpillars within the support material. The grid of pillars may be indirect contact with support material, and/or with a printing tray. Thecontroller may control constructing of at least one support constructionas a body outline around a printed object.

According to some embodiments of the present invention a printingapparatus for three-dimensional printing may include a controller todetect defective nozzles, and to adjust printing coordinates tocompensate for the defective nozzles. The controller may controladjustment parameters by print head shifting, print head movement,and/or input data conversion. Control of adjustment parameters may beaccording to a shift algorithm. The controller may enable printing afirst layer of an object to be printed by a printing head having acertain reference frame; and printing a second layer of an object to beprinted by said printing head, the printing head having a secondreference frame that is different from the first reference frame.

According to some embodiments of the present invention a printingapparatus for three-dimensional printing may include a controller toenable moving a printing head in a forward passage when printing anobject, and adjusting the height of a printing tray prior to the reversepassage of the printing head.

According to some embodiments of the present invention a printingapparatus for three-dimensional printing may include a controller toshift the step of a nozzle array, where said nozzle array includes alarge nozzle step. The controller may enable printing additional layersin a first direction, and lowering the printing tray for each additionallayer printed in the first direction. The controller may enable printingadditional layers in a second direction, where the number of additionallayers are related to the nozzle step divided by the size of the nozzledroplet stain.

According to some embodiments of the present invention a method isprovided for three-dimensional object printing that includes increasingadherence of an object being printed to a printing tray, wherein theprinting tray has predetermined surface characteristics. The printingtray may include an anodized layer, and may have pores that may befilled with material that attracts modeling material. The pores may befilled with water. The printing tray may be pre-treated with water.

According to some embodiments of the present invention adherence of anobject being printed to a printing tray may be increased by using aprinting tray that has a thermal coefficient substantially similar tothat of a printed object. The printing tray may be made of organicmaterial. The printing tray may be made from substantially similarmaterial to a printed object.

According to some embodiments of the present invention,three-dimensional object printing methods may include printing a supportconstruction below the base of an object to be printed, such that theconstruction adheres to the object and to a printing tray on which theobject is to be printed. An object may subsequently be printed on theconstruction.

According to some embodiments of the present invention a printing methodmay include printing a support construction as a barrier layer between aprinting tray and an object to be printed, such that the barrier layerseparates the lower layers of the object to be printed from the printingtray. An object may subsequently be printed on the barrier layer.

According to some embodiments of the present invention the temperatureof an object being printed may be controlled. The control may be enabledby heating a printing tray to a selected temperature during the buildingof the object. The object may subsequently be cooled. The selectedtemperature may be substantially at the glass transition point of amodeling material, or at the glass transition point of a supportmaterial. The temperature of an upper layer of material of an objectbeing printed may be controlled, by for example a controller, forexample, to a temperature above the glass phase transition of thematerial. Such control may be enabled using an electromagnetic radiationassociated with the curing device, electromagnetic radiation independentof the curing device, exothermic chemical curing, a heating element, acooling element, and/or other suitable temperature control elements,such as a temperature sensor and controller that operates the coolingand heating elements according to the sensor reading and requiredtemperature. The material of the upper layer(s) may be heated beforedepositing.

According to some embodiments of the present invention the temperaturein a printing sub-system may be controlled during a printing process,using, for example, a heating element, a cooling element, a curing unit,a radiation unit, an insulated printing sub-system, and/or othersuitable temperature control elements. The cooling of the printingsub-system may be controlled. The printing tray may be moved to aninsulation area, which may be, for example, within the printingsub-system or outside of the printing sub-system. The insulation areamay include a removable structure.

According to some embodiments of the present invention athree-dimensional object printing method may include printing a“thickening” layer comprised of a support structure of a predeterminedthickness around a printed object. The support structure may includesupport material, and/or a combination of support material and modelingmaterial either as a homogenous mixture or not The thickening layer maybe removed after printing is complete. The thickening layer mayadditionally help prevent the accumulation of excess material on thesurfaces of the object.

According to some embodiments of the present invention, a printingmethod may include printing a first layer of building material, curingthe first layer of material, and printing an additional layer after thefirst layer is cured. The printing tray may be positioned at a relativeheight or level that enables compensation for the shrinkage in thepreviously printed and cured layer.

According to some embodiments of the present invention a method ofpreventing mechanical deformation of a three-dimensional printed objectupon removal of the printed object from the printing tray may includeusing a printing tray with low adhesion characteristics.

According to some embodiments of the present invention a method ofpreventing mechanical deformation of a three-dimensional printed objectupon removal of the printed object from the printing tray may includeexposing the printing tray to cold water or other cooling means.

According to some embodiments of the present invention a method ofpreventing mechanical deformation of a three-dimensional printed objectupon removal of the printed object from the printing tray may includeexposing the tray to shock waves.

According to some embodiments of the present invention athree-dimensional object printing method may include printing a supportconstruction on a printing tray prior to printing an object, the supportconstruction including one or more layers of modeling materialprotruding outside the boundaries of the base of the object. Themodeling material may be covered with a support construction, which mayprotrude outside the boundaries of the object. A thin layer of modelingmaterial may be deposited over the support material. The supportconstruction may include a combination of modeling material and supportmaterial. The support construction may include one or more pillars ofmodeling material interspersed with support material.

According to some embodiments of the present invention athree-dimensional object printing method may include printing athree-dimensional object with an adjacent support construction separatedfrom the object by a barrier. The barrier may include at least one setof vacant pixels that may allow for the spread of modeling and supportmaterials into the vacant pixel barrier and thus reduce the mixing ofthe materials of each construction.

According to some embodiments of the present invention athree-dimensional printing method may include printing a supportconstruction that includes support material and modeling materialelements within the support material, to reinforce the support material.The support construction may include a grid of pillars within thesupport material. The pillars may be larger and/or more closely spacedat the outer periphery of the support construction. A wall of modelingmaterial may be constructed surrounding the support construction. Thesupport material may be, for example, interspersed with modelingmaterial elements. A continuous phase of support material may bereinforced by model material in the form of, for example, columns,membranes, and/or cubes. The support construction may be dispensed as,for example, a body outline around a printed object.

According to some embodiments of the present invention athree-dimensional object printing method may include constructing asupport construction on the printing tray; and printing an object on topof the support construction, such that the object may be built withinthe leveling range of a leveling device associated with the printingapparatus.

According to some embodiments of the present invention athree-dimensional object printing method is provided that includesdetecting problematic nozzles, and adjusting printing coordinates tocompensate for the problematic nozzles. The adjustment may includecontrolling print bead shifting in Y (e.g., the non printing direction),input data conversion, and/or other suitable adjustment parameters. Ashift algorithm may be used to adjust a printing head.

According to some embodiments of the present invention a method forhigher 3-D printing resolution in the Y-direction, than may be set forthby the droplet diameter may include printing a first layer of an objectto be printed, interlacing, and printing a second layer of an object tobe printed over said first layer. Each of the layers may include aportion of required pixels. The first layer and second layer havedifferent height values. A third layer may be constructed over thesecond layer. A shift algorithm may be used to perform the interlacing.

According to some embodiments of the present invention a method for 3-Dprinting may include adjusting the height of a printing tray prior tothe reverse passage of a printing head printing an object on theprinting tray, subsequently printing the reverse passage by the printinghead. The printing tray height may be adjusted.

According to some embodiments of the present invention, the step of anozzle array may be shifted, in the case, for example, where said nozzlearray has a large nozzle step. The shifting may include printingadditional layers in the X direction, and lowering the printing tray foreach additional X direction layer printed. The method may includeprinting additional layers in the Y direction, such that the number ofadditional layers are related to the nozzle step divided by the size ofthe nozzle droplet stain.

BRIEF DESCRIPTION OF THE DRAWINGS

The principles and operation of the system, apparatus, and methodaccording to the present invention may be better understood withreference to the drawings, and the following description, it beingunderstood that these drawings are given for illustrative purposes onlyand are not meant to be limiting, wherein:

FIG. 1 is a block diagram of a 3D printer system according to someembodiments of the present invention;

FIG. 2A is a schematic illustration of a printing tray and printingobject, according to some embodiments of the present invention;

FIGS. 2B-2E are flow chart illustrations of exemplary methods ofprinting, according to an embodiment of the present invention;

FIG. 3A is a schematic illustration of a printing sub-system, accordingto some embodiments of the present invention;

FIGS. 3B-3C are flow chart illustrations of exemplary methods ofprinting, according to an embodiment of the present invention;

FIG. 4A is a schematic illustration of a 3-D support structure with agrid, according to an embodiment of the present invention;

FIGS. 4B and 4C are schematic illustrations of interface lines in aprintable object, according to an embodiment of the present invention;

FIG. 5A is a schematic illustration of a process whereby “falloutmaterial” is formed;

FIG. 5B is a schematic illustration of various support constructions,according to some embodiments of the present invention;

FIGS. 6A-6D are schematic illustrations of support grids used forprintable objects, according to some embodiments of the presentinvention;

FIG. 6E is a flow chart illustration of an exemplary method of printing,according to an embodiment of the present invention;

FIG. 7A is a flow chart illustration of an exemplary method of printing,according to an embodiment of the present invention; and

FIGS. 7B-7E axe schematic illustrations of higher print resolutionprocedures according to some embodiments of the present invention.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the drawings have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the drawings toindicate corresponding or analogous elements throughout the serialviews.

DETAILED DESCRIPTION

The following description is presented to enable one of ordinary skillin the art to make and use the invention as provided in the context of aparticular application and its requirements. Various modifications tothe described embodiments will be apparent to those with skill in theart, and the general principles defined herein may be applied to otherembodiments. Therefore, the present invention is not intended to belimited to the particular embodiments shown and described, but is to beaccorded the widest scope consistent with the principles and novelfeatures herein disclosed. In other instances, well-known methods,procedures, and components have not been described in detail so as notto obscure the present invention.

It is noted that the term “building material” as used herein may includemodel or “modeling” material, support material, mixed material, and/orany suitable combination of materials used in the building, forming,modeling, printing or other construction of three-dimensional (3D)objects or models. Building material may include material used to createobjects, material used to modify such material (e.g., dyes, fillers,etc), support material, or other material used in the creation ofobjects, whether or not appearing in the final object. The terms“structure” or “construction” as used herein may include different typesand/or combinations of building materials. For example, supportconstructions may include pillars built from modeling materialsurrounded by support material. A construction including a single,homogenous material may also be regarded as a structure or constructionaccording to embodiments of the present invention. The term “object” asused herein may include a structure that includes the object or modeldesired to be built. Such a structure may, for example, include modelingmaterial alone or modeling material with support material. The terms“support” or “support construction” as used herein may include allstructures that are constructed outside the area of the object itself.The terms “layer” or “slice” as used herein may include portions of anobject and/or accompanying support structures optionally laid one abovethe other in Z direction. The word layer may also be used to describe athree-dimensional envelope or skin.

The printing system and system components according to embodiments ofthe present invention may be similar to and use or be based on aspectsof embodiments described in U.S. Pat. No. 6,259,962, issued Mar. 1,1999, titled “APPARATUS AND METHOD FOR THREE DIMENSIONAL MODELPRINTING”; No. 6,569,373, issued May 27, 2003, titled “COMPOSITIONS ANDMETHODS FOR USE IN THREE DIMENSIONAL MODEL PRINTING”, No. 6,658,314,issued Dec. 2, 2003, titled “SYSTEM AND METHOD FOR THREE DIMENSIONALMODEL PRINTING”; and No. 6,850,334, issued Feb. 1, 2005, titled “SYSTEMAND METHOD FOR THREE DIMENSIONAL MODE”, as well as U.S. patentapplication Ser. No. 10/424,732, filed Apr. 29, 2003, Publication No.2003/0207959, published on Nov. 6, 2003 titled “COMPOSITIONS AND METHODSFOR USE IN THREE DIMENSIONAL MODEL PRINTING”; No. 10/101,089, filed Mar.20, 2002, Publication No. 2002-0171177, published on Nov. 21, 2002,titled “SYSTEM AND METHOD FOR PRINTING AND SUPPORTING THREE DIMENSIONALOBJECTS”; and/or No. 10/336,032, filed Jan. 3, 2003, titled “DEVICE,SYSTEM AND METHOD FOR ACCURATE PRINTING OF THREE DIMENSIONAL OBJECTS”,all assigned to the common assignee of the present invention and fullyincorporated herein by reference. However, the printer system accordingto some embodiments of the present invention may also have otherconfigurations and/or other methods of operation. For example, theprinter system according to the present invention may include more thanone printing head, and/or more than one material dispenser, positioner,curer, imager, illuminator, leveler, sensor, cartridge, cartridge valve,etc. In further embodiments, layer-by-layer deposition need not be used,and other curing or solidifying methods may be used. The printing headmay include, for example, an ink jet head or another suitable materialdeposit system or dispenser.

According to various embodiments of the present invention, the materialsthat may be used may be similar to the materials described in theaforementioned U.S. patent and U.S. patent applications. For example,photopolymer materials curable by the application of electromagneticradiation or other materials suitable for 3-D object construction may beused. The photopolymer material may be of various types, including, forexample, a photopolymer modeling material which may solidify to form asolid layer of material upon curing, and a photopolymer support materialwhich may solidify, wholly or partially, or not solidify upon curing, toprovide a viscous material, a soft gel-like or paste-like form, and/or asemi-solid form, for example, that may be easily removed subsequent toprinting. The various types of photopolymer material may be dispensedseparately or in any given combination, according to the hardness and/orelasticity of the object desired to be formed or any of its parts, orthe support constructions required to provide object support duringconstruction. Materials other than those described in the above patentsand applications may be used.

The 3-D object being printed may consist predominantly of modelingmaterial and may or may not be combined with support material, invarying ratios and combinations, according to the strength, elasticityor appearance desired for the finished printed object. Such combinationof materials used for the building of the object or model itself istermed the “modeling construction”.

“Support constructions”, on the other hand, may consist predominantly ofsupport material, which may or may not be combined with buildingmaterial in varying ratios and combinations according to the desiredstrength, elasticity and so on of the support construction. Supportconstructions may be printed adjacent and/or around part/s or all of themodeling construction/s according to the purpose which the supportconstruction/s are to serve.

A third type of construction that may be printed is the “release”construction, which may consist predominantly of support material(optionally with a relatively small element of modeling material).Release constructions may not solidify or may solidify partially to forma relatively soft layer or layers of material, to enable easy releasefrom a printed object. For example, the release layer may be a viscousliquid material, paste-like material, gel-like material and/orsemi-solid material etc., according to the requirements of the objectand the purpose which the release layer may be to serve in the printingprocess.

U.S. Pat. No. 6,259,962 assigned to the assignee of the presentapplication and incorporated herein by reference, describes, inter alia,embodiments including an apparatus and method for 3-D object printing.The apparatus may include, for example, a printing head, for example anink-jet type printing head, having a plurality of nozzles through whichbuilding materials are dispensed, and a dispenser connected to theprinting head for selectively dispensing material in layers onto aprinting tray. The printing head may draw material from a reservoircontaining the material. The reservoir may be connected to the printinghead, and may supply the material via a tube or tubes to the printinghead. A common type of reservoir may consist of a container, such as acartridge, containing building material. Other types of reservoirs andfeed systems may be used. The apparatus may further include anelectromagnetic radiation mechanism for optionally curing each of thelayers of material deposited. The location of depositing, and the amountand/or type of material to be deposited may be controlled by theapparatus' controller as preprogrammed from a 3-D data file. The depthof each deposited layer may be controlled by selectively adjusting theoutput from each of the plurality of nozzles.

The building materials used in the process of construction of 3-Dobjects according to some embodiments of the present invention aredescribed in U.S. Pat. No. 6,658,314 and further in U.S. Pat. No.6,569,373, both assigned to the current assignee, and both of which areincorporated herein by reference. Briefly, in one embodiment there aretwo main types of building materials used: “modeling material” or “modelmaterial”, being the first building material substantially as describedin the aforementioned patent applications assigned to the currentassignee, and “support material”, being the second building materialsubstantially as described in the aforementioned patent applicationsassigned to the current assignee. Of course, other materials, othernumbers of materials and other combinations of materials may be used.

As described in U.S. Patent Application Publication No. 2002/0171177incorporated herein by reference, a relatively solid support structuremay be formed using modeling material, for example in the form of narrowvertical pillars joined by horizontal membranes, around, between, and/orwithin which support material may be dispensed. The support structure,when cured, may provide a semi-solid support construction for the 3-Dobject being built Support material may be dispensed alone and mayremain uncured for various purposes, for example, to form layers of‘release’ between the solidified object and its semi-solid supportconstructions for easy separation of the two types of construction afterprinting is complete.

U.S. Pat. No. 6,850,334, assigned to the current assignee andincorporated herein by reference, includes for example an embodimenthaving an apparatus in the form of a leveling device which may follow inthe path of the apparatus' printing head. This leveling device may serveto straighten the most recently laid layer of materials before curing,thereby narrowing each layer to its desired depth and ensuringconsistent ‘spread’ of the materials within the layer, in preparationfor the deposit of the next layer of materials. Excess interfacematerial gathered en route by the leveling device may be cleaned off theleveling device and disposed of after separate curing.

The various constructions comprising each layer (e.g., modeling, supportand/or release; as required) may be deposited in the same passage of theprinting head in the X-Y axes, according to, for example, apredetermined CAD configuration which may be converted, for example, toa Stereo Lithography (STL) format, and programmed into an apparatuscontrol unit. The CAD configuration may determine, for example, theamount of building material, the type of building material and variouscombinations of materials to be jetted from the nozzles, and maydetermine from which nozzle and at which points building material may bejetted from each nozzle during the course of deposit of a single layerof materials. Other data formats may be used.

When printing, the printing head may move in the X-Y direction,depositing the materials in the course of its passage over the printingtray or printing area, in a predetermined configuration. This forwardpassage of the printing head may be followed by curing of the depositedmaterial by a source of electromagnetic radiation. In the reversepassage of the printing head, back to its starting point for the layerjust deposited (point 0 on the X-Y axes), an additional deposition ofmaterials may be carried out, according to predetermined configuration.In the reverse passage of the printing head, the second part of thelayer thus laid may be straightened by a leveling device, for example, aroller or blade, which may, for example, follow in the path of theprinting head in its reverse movement, and then the thus straightenedlayer may be cured by means of electromagnetic radiation. Since themovement of the leveling device may follow the reverse route of theprinting head, the first part of the layer deposited in the printinghead's forward movement may be thicker than the second part of the layerdeposited in the printing head's reverse movement. CAD configuration ofthe final depth or height of each layer, for example, may take intoaccount the final desired thickness of each single layer after forwardand reverse movements of the printing head at each height of theprinting apparatus on the Z axis. Other movement, curing, and levelingsequences may be used. For example, a leveling procedure may beperformed at other times.

Once the printing head has returned to the 0 position (starting point)in the X-Y axes, the printing tray may be lowered in the Z axis to apredetermined height, according to the desired thickness of the layersubsequently to be printed, and the printing head once again may beginits movement in the X-Y axes as predetermined. The tray need not belowered. The starting position of the printing head may be adjusted inthe Y axis, for example, for further printing in the X axis at the sameZ height as the previously deposited layer.

As described above, adverse effects in printed objects may take ondifferent forms, for example, various deformations and/or defects in thefinished product. According to some embodiments of the presentinvention, methods and apparatuses may be provided that may help inimproving the quality, strength, appearance, and/or ‘finish’ of thefinal product. For example, these apparatuses and methods may help inpreventing deformation of 3-D printed objects, aiding construction usingsupport materials, and improving accuracy of printed 3-D objects, as aredescribed in detail below.

FIG. 1 is a block diagram of a 3D printer system 100 according to anexemplary embodiment of the present invention. 3D printer system 100 mayinclude, for example, a CAD module 102 or other design module,controller 105, and printing apparatus 140.

Controller 105, which may prepare the digital data that characterizes a3-D object for printing, and control the operation of the printingapparatus, may include, for example, a processor 110, a memory unit 115,software code 120, and a communications unit 125. Other configurationsmay be used for a controller or control unit. Control functionality maybe spread across units, and not all control functionality may be withinsystem 100. For example, a separate unit, such as a personal computer orworkstation, or a processing unit within a supply source such as acartridge may provide some control or data storage capability.Communications unit 125 may, for example, enable transfer of data andinstructions between controller 105 and CAD module 102, betweencontroller 105 and printing apparatus 140, and/or between controller 105and other system elements. Controller 105 may be suitably coupled and/orconnected to various components of printing apparatus 140.

Printing apparatus 140 may include for example positioner(s) 155,material dispenser(s) 150, material supply unit(s) 152, and printingsub-system 180. Printing sub-system 180 may include a printing box 145,and a printing tray 170. Printing box 145 may include printing head(s)146, printing nozzle(s) 147, leveler(s) 157, curer(s) 159, and othersuitable components. Positioner 155, or other suitable movement devices,may control the movement of printing head 145. Leveler or levelingdevice 157 may include, for example, a roller or blade or other suitableleveling mechanism. Printing head 145 may be, for example, an ink jethead or other suitable printing head.

Controller 105 may utilize Computer Object Data (COD) representing anobject or a model, for example, CAD data in STL format. Other data typesor formats may be used. Controller 105 may convert such data toinstructions for the various units within 3D printer system 100 to printa 3D object. Controller 105 may be located inside printing apparatus 140or outside of printing apparatus 140. Controller 105 may be locatedoutside of printing system 100 and may communicate with printing system100, for example, over a wire and/or using wireless communications. Insome embodiments, controller 105 may include a CAD system or othersuitable design system. In alternate embodiments, controller 105 may bepartially external to 3D printer system 100. For example, an externalcontrol or processing unit (e.g., a personal computer, workstation,computing platform, or other processing device) may provide some or allof the printing system control capability.

In some embodiments, a printing file or other collection of print datamay be prepared and/or provided and/or programmed, for example, by acomputing platform connected to 3D printer system 100. The printing filemay be used to determine, for example, the order and configuration ofdeposition of building material via, for example, movement of andactivation and/or non-activation of one or more nozzles 147 of printinghead 145, according to the 3D object to be built.

Controller 105 may be implemented using any suitable combination ofhardware and/or software. In some embodiments, controller 105 mayinclude, for example, a processor 110, a memory 115, and software oroperating instructions 120. Processor 110 may include conventionaldevices, such as a Central Processing Unit (CPU), a microprocessor, a“computer on a chip”, a micro controller, etc. Memory 115 may includeconventional devices such as Random Access Memory (RAM), Read-OnlyMemory (ROM), or other storage devices, and may include mass storage,such as a CD-ROM or a hard disk. Controller 105 may be included within,or may include, a computing device such as a personal computer, adesktop computer, a mobile computer, a laptop computer, a servercomputer, or workstation (and thus part or all of the functionality ofcontroller 105 may be external to 3D printer system 100). Controller 105may be of other configurations, and may include other suitablecomponents.

According to some embodiments of the present invention, material supplyunit(s) 152 may supply building materials to printing apparatus 140.Building materials may include any suitable kind of object buildingmaterial, such as, for example, photopolymers, wax, powders, plastics,metals, and may include modeling material support material and/orrelease material, or any alternative material types or combinations ofmaterial types. In some embodiments of the present invention, thebuilding materials used for construction of the 3D object are in aliquid form. Such materials may be similar to those described inembodiments of U.S. Pat. Nos. 6,569,373 and 6,658,314 U.S. PatentPublication No. 2003/0207959, all of the same Assignee, and incorporatedherein by reference. In an exemplary embodiment of the presentinvention, the modeling and/or support materials used are photopolymersthat may contain material curable by electro-magnetic radiation and/orelectron beams etc. The materials may come in different forms, textures,colors, etc. Other suitable materials or combinations of materials maybe used.

The 3-D object printing process as described in U.S. Pat. Nos.6,259,962, 6,658,314 and 6,569,373 and U.S. Patent ApplicationPublication 2002/0171177, all assigned to the current assignee andincorporated herein by reference, may include a method of printing a 3-Dobject on a layer-by-layer basis. For example, printing an object mayinclude dispensing modeling and/or support materials on a layer by layerbasis according to a predetermined configuration, from a plurality ofnozzles on the apparatus' printing head. The building material(s) may bedispensed at a given temperature in a fluid state to form a layer, andafter dispensing each layer may optionally be cured by, for example, asource of electromagnetic radiation. The building material(s) maysolidify as a result of curing and subsequent cooling.

Printed 3-D objects, however, may be deformed or have defects. Factorsthat may contribute to such deformations and defects may include, forexample, internal stress forces due to the photo-polymerization curingprocess, for example residual polymerization occurring after primarycuring of lower layers or accumulative stress gradients within theprinted object. Additionally, temperature variances between levels oflayers and/or between the laid layers and the internal apparatus‘environment’ may cause deformations in the printed object. Furthermore,mechanical forces, for example damage caused during removal from theprinting tray, may leads to deformations of printed 3-D objects. Variousembodiments of the present invention are provided to minimizedeformation of a printed object during and/or after the printingprocess.

For example, solidification of building material(s) may cause shrinkageof parts of the object or the whole object. In addition, cooling orother temperature changes of the material after it has been dispensedand cured may cause additional shrinkage. After a number of layers havebeen laid, there may be a difference between the uppermost, last laidlayers and the lower layers of material, both in temperature and in theextent to which the different layers have been cured. For example, theuppermost layers may be warmed by the curing radiation and by theexothermic chemical curing process that evolves. The lower layers, incontrast, may be cooler, as they may have had more time in which tocool, and may have been cooled in a colder environment as compared tothe upper layers. In addition, with each passing of the printing headover the 3-D object being built, repeated irradiation of the layersbeneath the uppermost layers of material may cause a difference in theextent of curing between the lower layers and the uppermost morerecently laid layers. These and other differences in temperature andcuring between upper and lower layers may cause stress between thevarious layers of the object, and may lead to a variety of deformations.Other embodiments may not experience such temperature differences orradiation differences.

One appearance of deformation that may occur is the lifting or ‘curling’of the base edges of the 3-D object upwards. This phenomenon may relate,for example, to the excess of repeated UV radiation that the sides areexposed to, which may cure the sides more than the center of the object.Curling up of the edges of the base of the object may also result fromthe lower temperature of the sides of the object, which may shrink inrelation to the center of the object. In other situations, the center ofthe object rather than the sides may lift, due, for example, to thestronger shrinkage of the lower layer with respect to the upper layers,as described above. Curing using methods other than UV may be used.

Another form of deformation that may occur is the sideways ‘bending’ ofvertical walls of the printed object. The sides of the object beingprinted may be exposed to repeated radiation (e.g., UV radiation) and tomore cooling than the center of the object. Furthermore, different sidesof the printed object may be exposed to different amounts of radiationand cooling etc. These influences, for example, may cause the object tobe elongated more on one side than the other, therefore causing thewalls to bend.

According to some embodiments of the present invention, components andmethods are provided to keep a printed object firmly adhered to theprinting tray, possibly minimizing or preventing deformation of a 3-Dobject during and/or after printing, and/or providing other benefits.

Reference is now made to FIG. 2A, which is a schematic illustration ofvarious support layers printing elements that may be provided, accordingto some embodiments of the present invention. Printing tray 170 may becoated with a surface coating 202, for example, an adhesive coating orlayer that has characteristics appropriate to enable high adhesion tothe object's building material(s). These characteristics may be, forexample, mechanical or chemical in nature. One type of surface coating202 may include, for example, an anodized layer (e.g., coatedelectrolytically with a protective or decorative oxide) laid over, forexample, a smooth aluminum surface. Another type of surface coating 202may include an anodized layer with pores that are filled with modelingmaterial or any other material that may chemically fit and attract themodeling material. An additional type of surface coating 202 may be ananodized coating with pores that are filled with water. Other suitablematerials and surface constructions may be used.

According to some embodiments, printing tray 170, and optionally surfacecoating 202, may require frequent cleaning with, for example, water (asopposed to solvents, e.g., alcohol) to increase adherence of thebuilding material to printing tray 170. Printing tray 170, according tosome embodiments, may require pretreatment with water.

According to some embodiments of the present invention, printingapparatus 140 may provide a relatively thin membrane, appendage, orcarpet 210 of building material below and/or around the base of theobject being printed 200. This appendage or carpet 210 to the base ofthe object being printed may include, for example, one or more layers ofmodeling material. In cases where carpet 210 may tend to lift from tray170, the portions of carpet 210 that protrude out of the boundaries ofthe base of object 200 may be coated with one or more layers of supportmaterial 215 that may protect carpet 210, for example, from additionalcuring, and may help keep carpet 210 flexible and adhesive in texture.In order to coat the carpet edges, one or more layers of supportingmaterial 215 may protrude outside the carpet's circumference therebycovering the carpet. In addition, above the layers of support material215, an additional layer or layers of modeling material 220 may be addedto strengthen carpet 210 during printing. Carpet 210, which may include,for example, soft and adhesive support layers above and around it, maybe effective, for example, in preventing air, radiation etc. frominfiltrating between the base of object 200 and tray 170, therebyhelping prevent detachment of object 200 from tray 170.

According to some embodiments of the present invention a supportpedestal 230 may be provided to help ease the removal of a printedobject from the printing tray and thus may help prevent deformation bymanual or mechanical damage. A support pedestal may be defined as a partof the support structure that may be lower than the lowest point of theobject. Support pedestal 210 may enable easy release of printed object200 from printing tray 170, may improve an object's accuracy in the Zdirection (height), and/or may improve an object's accuracy in the X-Ydirections. Support pedestal 210 may be provided, for example, byprinting extra support construction layers underneath the object and/orthe object's adjacent support constructions. The pedestal may be, forexample, a matrix of support construction layers that may bepre-configured to be printed beneath the object (e.g., between theobject and the tray). Such a support matrix may be printed prior to thelaying of the first layer of the 3-D object to be built, and may includesupport material and/or a combination of modeling, support, releaseand/or other materials. The supporting pedestal may be constructed frommodeling materials that, for example, may not tend to lift from thetray, and therefore may not be required to be firmly attached to thetray. Such modeling materials may, for example, be characterized bybeing soft and of a flexible nature. Support pedestal 210 may beconstructed from regular support construction, or may be more rigid andsticky so as to enhance adherence of the object to the pedestal. Suchconstruction may be composed, for example, of densely spaced thinpillars made of modeling material with support material in-between.Other suitable pedestal constructions may be used.

Inaccuracies in Z may occur at the lowest layers of the printed object.This may be because the top surface of the tray at Z start level (the Zlevel of the tray when printing starts) may not be exactly at a heightwhich enables the leveling device to reach and thus level the firstlayers deposited in the printing process, when the leveling device maybe at its lowest point (e.g., because of inaccuracy in adjustmentsand/or incomplete flatness and horizon of the tray etc). As a result,the lower layers of the printed object may not be leveled by theleveling device and therefore their thickness may be greater than thedesigned layer thickness, therefore increasing the height of the objectas printed in contrast to the object as designed. The use of a pedestalconstruction under the lowest point of the object may solve this problemby specifying that the height at which printing of the actual object maystarts may be the height at which the pedestal itself may besignificantly leveled by the leveling device.

According to an embodiment of the present invention, pedestal 210 mayprovide a barrier between object 200 and tray 170. Barrier layer 230 mayhave a structure of similar construction to the main support structure215, but not necessarily equal to support structure 215. For example,the barrier layer may be a relatively soft layer, and may measure, forexample, a few tenths of a millimeter in height. The barrier layer mayhave any other dimensions. The barrier layer may provide a barrierbetween the tray and the object, which may have dissimilar thermalcoefficients, such that lower layers of printed object 200 may not bedirectly exposed to the surface of tray 170. The usage of soft barriermay require the object to be constructed from modeling material thatdoes not tend to deform when not bound strongly to tray 170.

Reference is now made to FIG. 2B, which is a flowchart illustrating amethod for improved quality printing of 3-D objects, according to someembodiments of the present invention. As with all embodiments of themethod of the invention discussed herein, the apparatuses discussedherein can effect the embodiments of the method. For example, acontroller as discussed herein may control various aspects of a suitableprinter (e.g., a movement control device, a temperature control device,print heads, etc) to effect a suitable embodiment. Furthermore, othersuitable apparatuses may be used to effect various embodiments of themethod. As can be seen with reference to FIG. 2B, the method mayinclude, at block 20, printing a construction of building material, suchas a carpet, below and/or around the base of the object to be printed,such that the construction may help the object to be printed adhere tothe printing tray; and, at block 21, printing the object. Other stepsand/or series of steps may be used. The carpet or part(s) of the carpetmay be printed in the same X movement as the printing of the objectand/or its support constructions, or in alternative X movements, or in Yor Z movements.

During a printing process or after printing is finished, the bottomlayers of an object 200 and tray surface may cool simultaneously. In thecase where the tray is made of metal and the printing materials areplastic, for example, the thermal expansion coefficient of plastic maybe significantly larger than that of metal. In the case where there is astrong adherence of object 200 to tray 170, the bottom layers of object200 and the tray surface may shrink by a similar amount, since theobject shrinkage may be partially determined or controlled by the trayshrinkage, despite the large difference in the shrinkage coefficient ofthe two components. The amount that an object layer may shrink maygradually increase when the built layer is further apart from the tray.The difference in shrinkage between the bottom layers and the higherlayers may therefore introduce adverse stress in the printed object, andmay cause, for example, uneven dimensional errors in various parts ofthe object.

Reference is now made to FIG. 2C, which is a flowchart illustrating amethod for improved quality printing of 3-D objects, according to someembodiments of the present invention. As can be seen with reference toFIG. 2C, the method may include, at block 22, printing a barrier layerof building material between a printing tray and an object to beprinted, such that the barrier layer may separate the lower layers ofthe object from the tray; and, at block 23, printing the object. Othersteps and/or series of steps may be used. Other steps and/or series ofsteps may be used.

In another embodiment of the present invention, a tray 170 may beprovided that has a thermal coefficient similar to that of object 200.For example, tray 170 may be made of organic material or of the same orsimilar material to the object material, for example, a plastic that hasa thermal coefficient similar to that of the printed layers of buildingmaterial. It may be necessary, for example, for the organic material tohave a low thermal conductivity. The usage of such a material for tray170 may enable tray 170 to expand and/or contract at a rate equivalentto that of the building material, which may, for example, decrease thestrain and minimize deformation due to differences in thermaltendencies.

According to some embodiments of the present invention, printing tray170 may be warmed prior to printing of a 3-D object, to a temperaturethat is, for example, close to the glass transition point of themodeling and/or support materials, by, for example, a temperaturecontrol unit 204. Printing tray 170 may subsequently be allowed togradually cool down after printing, for example, causing a controlled,gradual cooling down of the initial printed layers. In this way thecured material of the initial layers may remain for a relatively longtime in near flow-able state, and may thus attain close contact with themolecular lattice of tray 170, resulting in firm adherence of theprinted object to the printing tray after solidifying. In otherembodiments, tray 170 may be heated before the start of printing to sucha temperature that the shrink of the tray and object during and afterprinting due to a temperature decrease are controlled to best fit eachother, for example, by shrinking to a substantially similar amount. Trayheating may be performed by temperature control unit 204.

Reference is now made to FIG. 2D, which is a flowchart illustrating amethod for improved quality printing of 3-D objects, according to someembodiments of the present invention. As can be seen with reference toFIG. 2D, the method may include, at block 24, heating printing tray 170,for example using temperature control unit 204, to a selectedtemperature, for example, such that the temperature may be substantiallyat the glass transition point of the modeling and/or support materials.At block 25 an object may be printed. At block 26, the tray may begradually cooled at a selected rate, using, for example, temperaturecontrol unit 204. In such a way adhesion of the object to the tray maybe enabled, and/or the respective shrinkage of the object and the traymay be controlled. Additionally or alternatively, tray 170 may be cooledusing temperature control unit 204, to enable adherence of an object totray 170. Other heating or cooling temperatures and/or mechanisms may beused. Other steps and/or series of steps may be used.

According to some embodiments of the present invention, a method ofpreventing and/or minimizing deformation caused by thermalinconsistencies between inner and outer parts of a printed object may beperformed by constructing a ‘thickening’ or outer covering of supportstructure of a predetermined thickness around the external surface ofthe printed object. This covering may, for example, shield the object'sexternal surfaces from disproportionate curing and/or uneven heating orcooling.

Reference is now made to FIG. 2E, which is a flowchart illustrating amethod for improved quality printing of 3-D objects, according to someembodiments of the present invention. As can be seen with reference toFIG. 2E, the method may include, at block 27, printing a thickeninglayer of building material of a predetermined thickness around theexternal surface of a printed object, and, at block 28, cooling theobject. Other steps and/or series of steps may be used.

Reference is now made to FIG. 3A, which is a schematic illustration ofprinting sub-system 180 or printing cell, which may include variousprinting components, according to some embodiments of the presentinvention. Printing sub-system 180 may include, for example, a blowingunit 330 and and/or a sucking unit 340, for respectively cooling ofprinting sub-system 180 by sucking hot air or other substances out ofprinting sub-system 180 and/or drawing cool air or other substances into printing sub-system 180 from the surroundings. Printing tray 170 mayinclude an adhesive surface coating 375, to enable adhesion of a printedobject to tray 170. Printing sub-system 180 may include a temperaturecontrol unit 310 and/or Temperature control unit 310 may include aheating source and/or a cooling source. Heating source may include, forexample, wires, heating elements and/or other suitable components.Cooling source may include, for example, wires, cooling elements,cooling tunnels, and/or other suitable components. Printing tray 170 mayinclude one or more cooling tunnels 380. Printing sub-system 180 mayinclude a temperature sensing unit 385, optionally associated withtemperature control unit 310, to sense the temperature of cell 180, tray170, building materials etc. Printing sub-system 180 may include anelectromagnetic radiation source 315, to enable heating of the buildingmaterial before, during, and/or after deposition. Printing sub-system180 may include an electromagnetic lamp 320, for curing and/or warmingof printed objects. Printing sub-system 180 may have insulationstructures, for example, insulation walls 350 and/or insulation layer(s)355. Insulation walls 350 and/or insulation layers 355 may be coated orlaminated internally by an insulation coating or covering 360, forexample, glossy aluminum foil or other suitable IR reflecting materials,to reflect the IR radiation. Printing sub-system 180 may have, forexample, a door or opening from which printed objects may be extracted.Printing sub-system 180 may include other suitable components orcombinations of components.

According to an embodiment of the present invention a method is providedto prevent and/or minimize object deformation, by printing in such a waythat the printing temperature of the upper printed layers may be above,for example, the glass phase transition temperature of the materials.The temperature control unit 310 and/or. Since curing, for example UVcuring, may occur at the uppermost layers of the printed object, thebuilding material in these layers may remain in a flow-able stateduring, for example, the entire curing time. When contraction takesplace in a liquid, the liquid may contract in a way that requiresminimum energy, which in this case, for example, may cause contractionalong the gravitational axis. Therefore the contraction may affect theheight of the material layer (Z axis). The lower material layers may bekept below the glass transition temperature in order to prevent collapseof the object under its own weight, or due to the machine's vibrations.

According to some embodiments, higher temperatures of the upper materiallayers may be maintained by various means, for example, by irradiatingthe upper layers using a warming electromagnetic radiation source 315,heating the building material before deposition, and/or warming theupper layers by heating element 312, the heat of the exothermic chemicalreaction of the curing itself, and/or any other suitable heating source.In one embodiment, a combination of preheated droplets of buildingmaterials, a strong electromagnetic lamp 320 which may include a UVwavelength required for curing, as well as visible and IR wavelengthsfor further warming, and/or a strong exothermic reaction, may raise andmaintain the required temperature of the top layers. Otherelectromagnetic sources may be used.

According to some embodiments of the present invention, a method ofpreventing and/or minimizing deformation is provided, that may includeincreasing the intensity of electromagnetic radiation such that curingof each subsequent layer of building material may be completed and/ormaximized prior to dispensing the subsequent layer of building material.

In cases where the temperature of the lower layers of the object and/orthe object's sides may be below, for example, the glass transitionpoint, further curing may cause shrinking of object material in the Zdirection as well as in the X-Y plane, which may introduce shear stressbetween the various layers. According to one embodiment the lower layersmay be warmed to prevent further curing of the object material, forexample, using UV or other radiation that may reach the lower layerswhen passing through the top layers, and/or may penetrate the bare sidesof the object.

Reference is now made to FIG. 3B, which is a flowchart illustrating amethod for improved quality printing of 3-D objects, according to someembodiments of the present invention. As can be seen with reference toFIG. 3B, the method may include, at block 31, heating up a higher layerof building material during curing; and, at block 32, cooling theobject. Other steps and/or series of steps may be used.

According to some embodiments of the present invention a method ofpreventing and/or minimizing deformation is provided, by lessening orminimizing thermal inconsistencies in the printed object. Such a methodmay include, for example, cooling each dispensed layer in turn afterprinting and curing, by blowing air on the top layer and/or sucking airfrom above the layer. Such cooling or sucking of air may be enabled, forexample, by using a suitable blowing unit 330 or sucking unit 340, whichmay be associated with printing head 145 or otherwise situated withinprinting apparatus 140. The method in one embodiment may not requirecooling the upper layers below the glass transition temperature, but mayrequire cooling of the top layers, for example, such that theirtemperatures do not exceed too high a value above, for example, theglass transition point.

According to some embodiments of the present invention, a method ofminimizing deformation is provided that includes printing with the airsurrounding the object at an even temperature which may be substantiallysimilar to the temperature of the top layers. Since the top layers maybe required to be, for example, of a temperature substantially similarto the glass transition point of the cured material, a substantiallysimilar temperature for the surrounding air and tray may beadvantageous. Other suitable temperature targets may be used. Forexample, a warmed tray may be used to warm up the air surrounding theobject during printing. For example, the printing sub-system 180 mayhave an insulated shield 355 and/or walls 350 to insulate printingsub-system 180, since printing sub-system 180 may be required to bewarmed by IR radiation in order to prevent cooling the object.Optionally, the inside of the printing sub-system 180 may have amaterial that may be reflective in the IR wavelength region. Accordingto one embodiment, the inner wall or side of the shield 360 may belaminated with, for example, glossy aluminum foil, to reflect the IRradiation. Other suitable materials may be used. An additional step inkeeping the environment warm may be to avoid opening printing sub-system180 while heating, cooling and/or curing may be taking place. Moreover,the object may be allowed to cool down slowly after printing hascompleted, for example, with the doors or alternative openings of theprinting sub-system remaining closed, so as to maintain nearly eventemperature outside and inside the object during cool down time.

During printing of an object, the layers of the building materials usedmay shrink within a short time interval, for example, a few seconds ortenths of seconds immediately after being laid and irradiated.Additional shrinkage may occur subsequently while cooling. When printingis paused, the shrinking before a next layer of material is dispensedmay continue for longer than usual, and as a consequence a thin ‘breakline’ or mark may be evident on the surface of the printed object.According to an embodiment of the present invention, a method ofpreventing and/or minimizing such ‘break lines’ may be provided, thatmay include keeping one or more layers previously deposited (before sucha pause) warm, for example, by exposing the layer to warmingelectromagnetic radiation during such a pause, until printing of thesubsequent layer resumes. Other methods of maintaining the warmth ofprinted layers may be used, for example, using heating element 312.Warming or other temperature control methods may have benefits otherthan or in addition to avoiding break lines.

In another embodiment, ‘break-lines’ between layers may be minimized orprevented by, for example, compensating the expected shrinkage in theZ-axis by altering the height of printing tray 170 prior to thedeposition of the next layer of material after printing is resumed. Forexample, printing tray 170 may be lowered to print a subsequent layer,but before printing of the subsequent layer, printing tray may beslightly raised to compensate for the excess shrinkage in the previouslayer. The previously laid layer may be leveled by leveler 157, and thenext layer may subsequently be deposited. Since the layer thickness orheight may be equal to the level of the bottom of the leveler minus thelevel of the top of the preceding layer, the correct layer thickness mayhereby be assured. The extent to which printing tray 170 may be loweredand/or lifted may be determined according to the length of the pause inprinting, and/or according to other printing parameters.

Reference is now made to FIG. 3C, which is a flowchart illustrating amethod for improved quality printing of 3-D objects, according to someembodiments of the present invention. As can be seen with reference toFIG. 3C, the method may include, at block 33, depositing a layer ofbuilding material. At block 34 the material may be cured. At block 35positioning a printing tray at a relatively high level, so as tocompensate for the shrinkage in the previously printed and cured layer,the uplifting being determined in accordance with the shrinkage in thecured layer. In one embodiment the printing head may be suitably movedso as to compensate for the shrinkage in the previously printed andcured layer. Other steps and/or series of steps may be used.

After the printing process has been completed, deformation of or damageto the printed object may occur during the cooling phase of the objectand/or while removing the object from printing tray 170. According to anembodiment of the present invention, a method is provided for preventingsuch deformations, which includes allowing the temperature of printingtray 170 and the surrounding environment (e.g., the air) to decreaseslowly, before opening the printing-cell and removing the object fromprinting tray 170. The method may include, for example, keeping printingsub-system 180 closed during cooling, thereby cooling the printed objectby natural heat loss from the object to the surrounding air, and fromthe surrounding air through the insulating cover of the printingapparatus to the outside environment. Forced airflow around the objectshould preferably be avoided to enable even and slow cooling of theprinted object before its removal from printing tray 170.

According to other embodiments, a method of preventing such deformationsmay be performed using a removable printing tray. Accordingly, printingtray 170 may be removed from the printing area of printing apparatus 140together with the printed object to an insulated area, within which slowcooling of the printing object may occurs, as described previously. Theinsulating area may be external to printing sub-system 180, and may be amoveable structure, for example, a box. The insulating area may includea shield or set of walls to prevent fast escape of heat, and a flat andopen bottom. When printing is complete, an operator, for example, mayopen the door to the printing sub-system and place the insulating boxover the tray so as to completely enclose the object, and then removethe tray and the object thus enclosed from the printing machine. In thisway direct exposure of the object to the outside air may be minimized.

According to still further embodiments, a method of preventing suchdeformations may be performed using an insulating chamber or areasituated within the printing apparatus, such that, for example, printingtray 170 bearing a printed object may be automatically moved from theprinting area to the insulating chamber without necessitating opening ofthe printing apparatus by an operator. Such an embodiment may enableautomatic continuation of the printing of a next object, once thecurrent printing ‘job’ is completed and a new printing tray has beenprepared. According to the current and/or previously discussedembodiment the printer may immediately resume printing of a new objectusing, for example, a replacement tray.

Deformation that may occur in the printing process may be caused byphysical damage to the printed object when being manually removed fromthe printing tray on completion of printing. Such deformation may beincreased, for example, when some extent of manual or mechanical forcemay be required in its removal.

According to another embodiment of the present invention, if the objectis well adhered to a tray, for example a metal tray, the tray may becooled, for example, by detaching the tray and submerging it in coldwater or an alternative cooling source. Additionally or alternativelycold water from outside or inside printing apparatus 140 may be made toflow within channels such as cooling tunnels 380 within the base of tray170. The difference in the thermal expansion coefficient between thethus cooled tray and the printed object may cause the object to separateeasily from the tray. According to one embodiment shock waves orvibrations may be imposed on the tray during or after cooling, toaccelerate the detachment of the printed object from the tray.

When a 3-D printed object cools down, the X-Y dimensions may decreaseaccording to the object's thermal expansion coefficient. The lower partof the object which may be firmly attached to the printing tray mayshrink, however, according to the thermal expansion coefficient of thetray, which may be substantially different from that of the modelingmaterial. As a consequence the accuracy of the final X-Y dimensions atthe top of the object and at the bottom of the object may differ fromeach other. Improved printing accuracy in the X-Y directions may beenabled by, for example, incorporating a soft pedestal between the trayand the object to enable the bottom of the object shrinking to be inaccordance with the object's thermal expansion coefficient.

In an alternative embodiment, the bottom layer of the object may bemodified to partly include, for example, pixels or other areas ofsupport material, which may reduce the adherence of the object to thetray. In other embodiments the bottom layer of the object may be clearof support pixels (e.g., may preferably not include support pixels) soas to increase the adherence of the object periphery to the tray, sincedetaching of the object from the tray during printing may start at theperiphery, The density of support pixels may be determined in such a waythat the object may adhere to the tray as required, while detachment ofthe object from the tray after printing may still be relatively easy.

The printing of three-dimensional objects may require different types ofsupport constructions. These may be, for example, ‘supportconstructions’ and/or “release constructions” etc., as depicted inembodiments in U.S. Pat. Nos. 6,658,314 and 6,569,373 both of which areassigned to the current assignee and incorporated herein by reference,and as described hereinabove. “Support constructions” may consistpredominantly of support material that may or may not be combined withmodeling material in varying ratios and combinations according to thedesired strength, elasticity and so on of the support construction.Support constructions may be printed, for example, underneath and/oradjacent to the modeling construction(s), according to the purpose whichthe support construction(s) are to serve. “Release constructions” asdescribed above may consist predominantly of support material,optionally combined with a relatively small proportion of modelingmaterial, and may be deposited between the modeling construction and itsadjacent support construction(s). Curing may solidify releaseconstructions to provide, for example, a relatively soft layer ofmaterial. Such a layer may be, for example, viscous liquid, paste-like,gel-like or semi-solid to varying extents, as required, in order to easethe separation or ‘release’ of the support construction from the objectafter printing. Support and release constructions other than thosedescribed in these applications may be used.

The support and release constructions, respectively, may serve thepurposes suggested by their names: ‘support constructions’ may be built,for example, to support parts or the whole of the object beingconstructed and to prevent the modeling construction from collapsingonto the printing tray. For example, where one surface of the object isconstructed at a less than 90° angle, a support construction may beconstructed ‘underneath’ this surface to support its construction.Another example may be where part of the object is constructed only froma certain Z-level (height), such as a part branching off the main bodyof the object or a ‘lid’ on top of an open object, a ‘supportconstruction’ may be built up to the Z-level where construction of thispart of the object begins. ‘Release constructions’ may for example beprinted between the modeling construction and the supportconstruction(s) to, for example, enable easy release of the supportconstruction/s from the object. Support constructions may also serve,for example, to prevent the object being knocked by the leveling device,modify curing on the object's side walls, improve object surfacequality, and reduce deformation etc.

U.S. Patent Application Publication No. 2002/0171177 incorporated hereinby reference, describes, inter alia, embodiments including variouspossible types of support constructions. For example, a relatively solidsupport structure may be formed using a skeleton, grid, or framework ofmodeling material or modeling construction, for example in the form ofvertical pillars, bases, columns or other suitable structures,optionally joined by horizontal membranes, also of modeling material ormodeling construction, around, between, and/or within which supportmaterial or support construction may be dispensed, and which structurewhen cured may provide a semi-solid support construction for the 3-Dobject being built. The thickness or width of the pillars and/ormembranes and their placement and/or distances between them, may dependon the size and shape of the object being built. Other suitable supportstructures may be used.

Reference is now made to FIG. 4A, which is a schematic diagramillustrating a grid or skeleton of structures within a supportconstruction, according to some embodiments of the present invention. Ascan be seen in FIG. 4A, support construction 400 may include aperipheral grid, for example, a skeleton of pillars and/or membranes405, that may be, for example, substantially constructed from modelingmaterial. Peripheral grid 405 may be larger and/or more closely spacedthan the pillars and/or membranes 410 within the ‘body’ of supportconstruction 400. These grid elements may provide additional strength tosupport construction 400. In one embodiment a peripheral grid orstructure may be in the form of a thin wall of building or modelingmaterial surrounding a support construction, to give extra strength tothe support construction. For example, in cases where the supportconstruction itself is very soft and not able to retain its own shape,e.g., when the support construction consists mainly of a certain type ofsupport material, such a grid may be required. Grids or skeletons mayinclude pillars, bases, columns, or other suitable structures.

Reference is now made to FIG. 4B, which is a schematic illustration of a3-D object 40 with adjacent support construction(s) according to someembodiments of the present invention. When building a 3-D object 40, thematerials making up the modeling construction 41 and those making up thesupport construction 42 may tend to merge into one another where the twotypes of construction meet. Such a meeting of material may lead to theformation of an interface line 44. Such an interface line 44 may, forexample, weaken the final object's walls and reduce the hardness andglossiness of the final object's surface

Reference is now made to FIG. 4C, which is a schematic illustration of a3-D object 40 with adjacent support construction(s) according to someembodiments of the present invention. As can be seen with reference toFIG. 4C, a “barrier” 46 may be constructed, for example, from an area ofvacant pixels, where no building material may be deposited. Such abarrier 46 may be constructed between the object construction 41 and thesupport construction 42 to prevent merging of materials at interfaceline 44. Such a barrier 46 may enable absorption of materials from eachconstruction type into the barrier 46, as opposed to the materialsspreading into each other, while at the same time providing a line ofseparation between them. In this way, the thickness of the interferenceline 44 may be reduced. The size of the barrier space may vary. Forexample, the barrier space may be equivalent in size to a slice rangingbetween ¼ of to 4 times the droplet diameter, after the depositeddroplet has spread to its final diameter on the printing surface (thesurface of former printed layer). Other dimensions may be used.

Support constructions can be used in a number of ways to help improvethe external appearance of the 3-D object and/or to prevent problemsthat may arise in the building of various 3-D objects. Vertical surfacesof printed 3-D objects may be of lower quality than non-verticalsurfaces, for example, because part of the droplets aimed at the rim ofeach layer may miss the edge of the layer and fall to the tray surfaceor slide downward on the vertical surface of the object. Additionally oralternatively the edges at the top of the partially built object may beslightly rounded because of the surface tension characteristics of theliquid modeling material, possibly causing the top layer of the objectto be shorter than as designed

Reference is now made to FIG. 5A, which is a schematic illustration of a3-D printing system, according to some embodiments of the presentinvention. As can be seen with reference to FIG. 5A, the printing head500 may jet material 520 while moving over the printing area 540 in themain movement direction X. Therefore the building material 520 fromprinting head 500 may be jetted slightly off from the downward directiondue to the movement of printing head 500 in the X direction.Additionally or alternatively, since the top edge of the object 560 maybe rounded at the edges, the droplets of materials that are jetted justbefore printing head 500 leaves the object region may miss the objectand be located, for example, adjacent to object 560.

Furthermore, when using some curing, systems and material at the edge ofan object layer may not be cured well due, for example, to an excessiveamount of oxygen diffused from the surrounding air into the material,inhibiting the curing process. In some cases the uncured material mayflow down on the vertical wall and accumulate at different levels on thesides of the object, leaving shapes on the object's vertical surfaces.When the surfaces are cured the shapes that have been created on thewalls may remain. Such accumulations as on the vertical surfaces and/oron the ground are herein referred to as “fallout material”.

According to an embodiment of the present invention, such falloutmaterial may be prevented or minimized by constructing a supportconstruction, for example, an envelope, container or other suitableconstruction around the sides of an object (e.g., in one embodimentadding a ‘thickening’ layer to the vertical walls). This may be referredto as a ‘thickening layer’. Such a construction may cause falloutmaterial to accumulate on the sides of the support layer, or may causefallout materials to be absorbed into the support layer, and not on thesides of the object itself. In this way, the accumulated falloutmaterial may be removed from the object together with the supportconstruction after printing. Furthermore, the supporting envelope mayshield the object wall from air and may thus prevent the diffusion ofpossibly inhibiting oxygen, for example, into the modeling material. Inthis way the wall's edge may be cured more efficiently and the modelingmaterial may be prevented from flowing down to, for example, createwaves. Moreover such support envelopes or structures may reduce roundingof the top edges of the object. This may be useful, for example, whenprinting an object with 90° edges.

In other embodiments, thickening layers may also be used to help eventhe finished object surfaces. Object surfaces which are in contact withsupport construction during printing may have a “matte” appearance afterprinting has been completed and the support structure has been removed,while surfaces that were not being supported may appear more glossy. Theuse of a thickening layer, for example, a thin layer of support aroundthe entire object, may also prevent the formation of visible break lines(e.g., thin protrusions) on the object surface between areas that werein contact with support construction and those that were not.

In some embodiments, a thickening layer(s) may be used to prevent rolleror leveling device knocking, wherein leveling device 157 such as aroller or blade may collide with a printed object. When the levelingdevice enters the object area there may be a slight knocking. When theknocking is relatively strong, deformations may result, for example,thin object walls may be broken, and large areas of the printed objectmay be deformed, for example, may be wavy, as a result of levelingdevice oscillations brought about by knockings.

In general when printing, the interface material laid at the uppermostsurface of the object may tend to take on a rounded shape at the edgesof the object. However, this ‘rounding’ may be significantly morepronounced when printing thin walls and/or pins like shapes. As aconsequence, the ridge or center of the thin wall may be higher thanexpected. Since a printing movement in the backward direction of X maybe followed by leveling action of a leveling device 157, which may beattached to a printing block, for example, behind the printing head. Anyleveling, however, may not follow printing movement in the forwarddirection, which may result in part of an object, for example, a wallridge, being built and cured to a higher height than designed during theforward direction. As a result leveling device 157 may collide with theobject wall during the backward movement. Adding a ‘thickening’ layer atboth sides of the thin wall may prevent rounding and therefore preventcollision or knocking of the leveling device with the top of the wall.

Knocking may occur even when printing thick objects, for example, whenprinting thick walls that are perpendicular to the printing direction X.This may be due, for example, to movement axles that are not stiffenough. With such non-rigid axles, such very slight collisions that mayunavoidably happen when the leveling device enters the object area mayinitiate leveling device oscillation in the Z direction. Strongoscillations may result in strong knocking. Thickening may lessen theinitial collision by smoothing the pressure step function that theleveling device may “sense” when entering the object area, thereforelessening or preventing the onset of leveling device oscillations. Othersequences of movements, for example, not requiring backwards andforwards movements, may be used.

According to one embodiment, one or more support constructions may beconstructed around an object, thereby providing a body outline. A bodyoutline, as can be seen with reference to FIG. 5B may include one ormore constructions or layers, in any combination. For example, an objectconstruction 50 may be surrounded or partially surrounded by an airbarrier layer 51. Air barrier layer 51 may help, for example, to preventmerging or mixing of modeling and support materials etc. A softconstruction layer 52 may be built, to enable easy removal of a supportconstruction from an object. A support construction 53 may be built,which may help in preventing a projection of coarse grid from, forexample, a bulk support construction, on the object's surface. Bulksupport material 54 may be dispensed as a layer or mass of material, toprovide support for object construction 50 or support constructions. Aperipheral support construction 55 may be built, for example, toreinforce support construction 54. Such a peripheral supportconstruction 55 may enable provision of sufficient support for object50, possibly at a minimal cost, and enabling easy support removal. Apedestal support construction 56 may be built, which may act like abuffer between the printing tray 170 and object 50. Pedestal supportconstruction 56 may help prevent deformation, by, for example,decreasing the difference of scale accuracy between the bottom and uppersides of object 50, helping ease detachment of object 50 from tray 170,and/or helping enable accurate leveling of the lower layers of object 50by leveler 157. One or more of the above described support constructionsmay enable, for example, separation of printed object 50 from the tray,separation of printed object 50 from its support constructions, and/orreinforcement of the object construction.

In one embodiment, a body outline, which may be a reinforced layerconstructed around a printed object, may be constructed within a supportconstruction. A support construction may include a number of bodyoutlines. For example, one body outline may surround a second bodyoutline, or may be located hi any other suitable location relative toone or more other body outlines. A body outline may, for example,include a grid or other suitable support constructions. Each such bodyoutline may or may not have a different grid. For example, a first bodyoutline adjacent to an object construction may be a thin layer ofsupport material or another suitable support material. For example, alayer of approximately 500 microns or other suitable dimensions may beused. Surrounding this first body outline, a second, optionally thickerbody outline may be constructed, for example about 3 mm thick or havingother suitable dimensions. Third, fourth, fifth etc. types of bodyoutlines may be subsequently constructed. Each body outline may serve apurpose in improving construction, quality and/or appearance of aprinted object. For example, the first body outline may enableseparation of the object from the support constructions. The second bodyoutline may, for example, produce a uniform surface, which may used toprovide required object-surface quality. The third body outline may, forexample, be constructed using a relatively high modeling material tosupport material ratio, therefore providing a more solid or rigidbuilding matrix. This third body outline, for example, may or may not bethicker than the second outline type. The fourth body outline, forexample, may include a relatively soft grid, and may facilitate removalof large masses of support material. Other types of body outlines orcombinations of body outlines may be used.

Taking into account the possible advantages of each type of bodyoutline, different objects may require different kinds of body outlines.For example, an object requiring a larger mass of support may benefitfrom further body outlines. For example, a ring approximately 10 mm highmay benefit from body outlines 1, 2 and perhaps 3. For example, acellular phone approximately 20 mm high may benefit from body outlines1, 2, 3 and 4. Preferable combinations of body outlines may bedetermined according to the object being built and the relativeadvantages and disadvantages of each type and/or combination of bodyoutlines.

Reference is now made to FIG. 6A, which is a schematic diagramillustrating a grid construction 600 that may be implemented as, forexample, a “support construction”, according to some embodiments of thepresent invention. Such a grid construction 600 may be defined as aconstruction that may include support material reinforced by discretemodeling material elements or areas. For example, a grid construction600 may be constructed by constructing one or more continuous supportmaterial layers 610 that may be reinforced by one or more continuouscolumns, bars, or pillars of modeling material 620. This kind of supportconstruction, which may include continuous modeling material areas, isherein referred to as a “Normal continuous grid”. The CAD software, forexample, which may provide instruction to printing system 100 toconstruct grid constructions, may enable construction of various typesand forms of grids, for example, “body outline grids”, “multiple griddesigns”, and “contacting grids” etc., as are described in detail below.Such additional grid improvements may be generally referred to herein as“smart grids”. The various methods and structures describe herein may beaffected by a system controller 105 associated with software 120.

According to an embodiment of the present invention, a multiple gridtype support construction may be constructed by defining, for example,grid widths (e.g., GRID WIDTH1) for X, Y and/or Z-axes, and grid spaces(e.g., GRID STEP1). These definitions may produce, for example, acontinuous area of support material reinforced by a continuous ornon-continuous grid constructed from modeling material. GRID Step 1 may,for example, be defined as the distance (in each one of the 3 axes)between modeling grids as defined by GRID WIDTH1, where GRID WIDTH1 maydefine the dimension (in each axis X, Y and Z) of the reinforcingmodeling elements included in the support construction.

Reference is now made to FIG. 6B, which is a schematic illustration of agrid construction, according to an embodiment of the present invention.As can be seen with reference to FIG. 6B a second definition, includingfor example, GRID STEP2 and GRID WIDTH2 for X, Y and Z may be defined.Such a definition may be applied to grid construction 600 resulting fromthe modeling grids defined by GRID STEP1 and GRID WIDTH1. Thedefinitions of, for example, GRID STEP2 and GRID WIDTH2 may produce, forexample, a continuous medium made of support material between the grids,and a non-continuous modeling grid made of the resulting grid as definedby GRID STEP2 and GRID WIDTH2. In this way, each grid (e.g., reinforcingelement) defined by GRID STEP2 and GRID WIDTH2 may be constructed from agrid mass as defined by GRID WIDTH1 and GRID WIDTH2. In some embodimentsGRID STEP1 may be thinner than GRID STEP2, as each grid defined by GRIDSTEP2 may include the resulting supporting construction formed by GRIDSTEP1. In some embodiments GRID WIDTH1 may be smaller than GRID WIDTH2,as each grid defined by GRID WIDTH2 may include the resulting supportingconstruction formed by GRID WIDTH1.

Such a grid, as described above (e.g., with non-continuous modelingelements), may enable the definition of “X”, “Y” and “Z” modeling griddimensions (e.g., GRID WIDTH), as well as the “X”, “Y” and “Z” distancesbetween modeling grids (e.g., GRID STEP). In one embodiment Z-step mayequal zero, which may result in the grid including continuous modelingcolumns (see FIGS. 6A and 6B). In another embodiment, as can be seenwith reference to FIG. 6C, Z-step may not be zero, which may resultingin non-continuous grid columns, with at least one gap 630 between gridcolumns. Directions “X”, “Y” and “Z” are used by way of example. Othersuitable directions or direction variables may be used.

In another embodiment, the gap 630 between modeling grid elements (e.g.,sticks and columns), which are referred to herein as “Modeling Gridbreak”, may not necessarily occur at the same locations for the variousmodeling elements. Such a case may result in a grid construction thatmay include a non-continuous grid, where each grid line may have gaps orgrid breaks 630 at different locations, as can be seen with reference toFIG. 6D. For example, a normal non-continuous grid as illustrated inFIG. 6C may produce a weaker Z-axis support construction than thecontinuous grid illustrated in FIG. 6A. However the Z-axis supportconstruction of FIG. 6C may produce a stronger Z-axis supportconstruction than the non-continuous Grid illustrated in FIG. 6D. Anon-continuous grid, such as the grid illustrated in FIG. 6D, mayprovide stronger X and Y-axis support, for example, than the normalnon-continuous grid of FIG. 6C, by, for example, assuring that amodeling grid break does not form at the same locations in the variousmodeling material elements. A non-continuous smart type of Grid mayresult, for example, in an improvement in support removal, compared tothe normal continuous type of grid. In other embodiments the diameter ofthe modeling grid elements may be increased without substantiallynegatively effecting the support removal from a printed object andwithout substantially negatively affecting support removal properties.

It should be noted that when used herein the X, Y and Z directions maybe relative to each other, and need not be absolute, and further the useof descriptions of movement in these directions is by example only, andother movement patterns and schemes are possible. Further, someembodiments described herein include a print head or other equipmenthaving a certain movement pattern (e.g., forward and backwards, etc), ora certain timing pattern of movement relative to jetting, curing, etc.These movement and timing patterns are shown by way of example only.Other suitable movement and timing patterns may be used.

In another embodiment, a further definition, including for example, GRIDSTEP3 and GRID WIDTH3 for X and Y may be defined. Such a grid may, forexample, be constructed so as to transcend the body outline and makecontact with the printed object itself. In this way, for example, such agrid may impart to the printed object high adhesion of the entiresupport construction. Usage of such grid constructions may help ineliminating or significantly reducing the possibility of the modelingconstruction being separated from the support construction(s) during orafter printing. For example, the grid Width definition and the grid gapdefinition may be significantly increased (e.g., GRID Width 3-1, GRIDStep 3-1) at a grid base, to cover an area that may come into contactwith the printing tray. Grid width definition may be significantlydecreased (e.g., GRID Width 3-2), at a grid end, to cover an area thatmay come into contact with the object, to enable relatively easy releasefrom the object. Additionally, between, for example, GRID WIDTHs 3-1 and3-2, the column (GRID) dimension may gradually be changed, for example,the grid column may taper, thereby narrowing significantly towards theend of the grid, where the grid meets the object. Other suitable griddefinitions or combinations of grid definitions may be provided.

Inaccuracies and/or imperfections in the final printed 3D object ormodel may occur for a number of reasons. Even if the inaccuracy isminimal, the error may have serious consequences for example, when twoor more parts are designed to fit together, a slight inaccuracy rendersthis impossible. According to some embodiments of the present invention,in order to limit the inaccuracy to a proportion acceptable in the art,e.g. 0.2 mm, or even smaller proportions, modifications may beintroduced to the configured data (for example the STL file) taking intoaccount the parameters of printing apparatus 140, the printing processand the building materials being used.

Imperfections in 3-D printed objects may occur for example, when one ormore nozzles 147 on printing head 145 are wholly or partially blocked,defective or non-functional. According to some embodiments of thepresent invention, if these problematic nozzles remain non-functionaleven after purging or other treatment, they may be defined in theapparatus controller 105 as “missing nozzles”, which may be compensatedfor during the printing process. An apparatus and method of detectingsuch “missing nozzles” is described and exemplified in PCT ApplicationNumber PCT/IL03/00746, filed Sep. 11, 2003, titled “APPARATUS AND METHODFOR CALIBRATION IN THREE-DIMENSIONAL MODEL PRINTING”, of the sameAssignees, which is incorporated herein by reference in its entirety.

In one embodiment the effect of missing nozzles may be spread over agreater area by, for example, shifting printing head 145, for example,in the Y-direction between printing cycles. The range of shift may needto be wide enough to be effective in compensating for the printing lackcaused by missing and/or defective nozzles, but still small enough toprevent significant errors in drop deposit placement due to ‘linearity’errors in the Y-axis. Other types of shifting may be used, and in otherdirections. Random shifts (e.g., within a predefined shift range) may bemade in between layers or within layers (e.g., in the reverse directionof the printing head). By using such shifting of printing head 145, andby taking into account the design of the object as defined in the data(e.g., CAD, COD or STL file etc.) and a map of missing nozzles asdefined in the data, printing apparatus 140 may avoid printing two ormore successive layers with missing nozzles in the same location. In thecase where a group of missing nozzles exists, special compensation stepsmay be taken, for example, defining a shift algorithm to overcome thelack in a specified area of printing head 145.

For example, the printing head may be shifted between passes to preventfull or partial overlap of, for example, the Y location of a the groupof missing nozzles in two or more consecutive layers. If a missing groupof nozzles is located at one of the two end points of the printing headmovement, for example, the effective size (length) of the head may bereduced by excluding a portion of the end from participating inprinting. The system controller 105 may for example calculate print datausing a smaller-sized printing head, and/or omitting missing ormalfunctioning nozzles. In such cases, each layer may be printed twiceor more, for example, where the printing head is shifted in the secondor subsequent prints from the first, in such a way that the missinggroups may not overlap in successive prints.

In another example, missing nozzles may be compensated for by using asystem of ‘back interlacing’. Controller 105 may, for example, introducea shift of printing head 145, for example, in the Y direction before itsbackward/reverse passage over the printing area in the X axis, takinginto account the map of missing nozzles defined in the STL file, tocompensate for missed pixels in the object. Controller 105 may use orcalculate adjustment parameters, including for example, variousdimensional adjustments, shifting of the print head, alterations toprint head movement, and/or alterations in the way that the input datamay be converted, to print data.

According to some embodiments of the present invention a number ofadjustments to the X, Y and/or Z-axes may be configured in the STL fileor other suitable data file, to help achieve a higher quality product,both in strength and in appearance. In one embodiment higher resolutionof each printed layer may be obtained by ‘interlacing’ successive layersof building material. For example, slight adjustments may be made to theprinting head's positioning in the X and Y-axes at each new Z level,such that drops of building material may fall ‘in between’ dropsdeposited in the previous forwards/backwards motions of the printinghead, thus interlacing layers of building material. In one embodiment,the interlacing may involve, or may be the functional equivalent to,printing a layer where the printing head has a certain reference frame(e.g., starting coordinate); and printing a second layer with a secondreference frame, the second reference frame being different from thefirst reference frame. Any suitable number of subsequent layers may beprinted, each layer having a reference frame that may or may not besimilar to other reference frames. For example, the reference frames maybe shifted slightly, and in the case where two or more such layers areprinted, the reference frames may be repeated.

In another embodiment, higher resolution may be obtained by sendingdifferent information to the printing head for each Z-movement of theprinting head. Whereas the forward and backward movements (e.g., X and Ymovements) of the printing head are usually at the same Z height, anadjustment may be made in the Z-axis prior to the reverse passage of theprinting head such that the layer deposited during the reverse passagemay be slightly removed in the X, Y and/or Z axes to, for example,further increase accuracy of the printing object This embodiment may beespecially practicable when printing an object that may be curved inshape in the Z-direction.

Reference is now made to FIG. 7A, which is a flowchart illustrating amethod for 3-D object printing that may enable compensation fornon-functional or problematic nozzles, according to an embodiment of thepresent invention. As can be seen with reference to FIG. 7A, the methodmay include, at block 70 detecting problematic nozzles. For example, anozzle test procedure may be executed periodically or randomly, inwhich, for example, the printing head may be operated for one layer anda test series, for example, a series of small bars, may be printed foreach nozzle. An operator or nozzle detector unit may detect missing orproblematic nozzles by checking the printout. Such a printout may bedone on tray 170, on a paper sheet attached to tray 170, or on anothersuitable medium. The data indicating the status of nozzles may beprocessed by controller 105, and, at block 705 the printing coordinatesfor the object to be printed may be adjusted, to compensate for theproblematic nozzles. Other steps and/or series of steps may be used.

Reference is now made to FIG. 7B, which is a schematic illustration of aprinting apparatus, according to an embodiment of the present invention.In cases where printing is executed with a nozzle array 800 with a largenozzle step, for example, where the space 810 in between nozzles islarger than the droplet diameter, gaps 830 may be evident between thetracks 820 of deposited material, which may cause the surface(s) of theobject to be uneven in texture or ‘finish’, e.g., stripe-like tracks maybe apparent on the surface of the printed object. According to anembodiment of the present invention, such gaps 830 between tracks ofdeposited material 820 that may be evident after, for example, a first Xprinting motion, may be filled by shifting the nozzle array 800, forexample, by a half-nozzle step in the Y direction before a next Xcomplementary printing motion. For example, if the first motion is inforward X direction, the second may be in backward X, and vice versa. Iftwo complementary X motions, as described above, are not sufficient forfilling the gaps between printing tracks, more complementary X motionsmay be used, optionally with smaller Y shifts between each. For example,3 motions with a ⅓-nozzle step shift, or 4 motions with a ¼ nozzle stepshift etc., may be used in the same layer. Since the nozzles may differfrom each other in their intensity, and some of the nozzles may be“dead”, lines of high and low accumulated material, or areas of missingmaterial may be formed. According to one embodiment, the Y location ofthe head (or nozzle array) may be toggled between the different printingmovements in the X direction. For example, random Y shifts may beexecuted, or non-random shifts, as determined by controller software120. This procedure is herein referred to as “nozzle scatter”. In thisway a Y shift associated with “nozzle scatter” may be used in order toimprove uniformity of the printed surface and compensation for missingnozzles.

Reference is now made to FIG. 7C, which is a schematic illustration of aprinting apparatus according to some embodiments of the presentinvention. A printing block 700 may include one or more curing sources710, for example, UV lamps. A leveler 720, for example, a levelingroller, may be designed in a way that it may only operate on theprinting material before solidification of the material. Since leveler720 may be located on the right side of jetting head or nozzle array715, in the illustrated example, the leveler may only be enabled totouch the material layer when an X motion of the head is from right toleft. Therefore, in order to assure that the roller does not touch thelayer during an X movement from left to right, a minor downwardcorrection of the height position of tray 730 may be performed before anX motion from left to right, for example, 100μ downward. It should benoted that the notions “X and Y motions of the head assembly” may referto motions relative to tray 730. Therefore X motion to the left may bedone by moving tray 730 to the right in respect to the axes of earthwhile jetting head 715 is stationary, etc. The same principal may referto Z height or motion of the tray, which may refer to the height ormotion of the tray relatively to head 715 position or motion. In anotherembodiment the size of the resolution pixels in the Y direction may beset equal to Y nozzle step or the Y minimal step between the X movementscomprising a slice (e.g., half-nozzle step or third or quarter steps,etc. as described above).

According to a further embodiment, since some nozzles may not befunctioning at a given time, a procedure of shifting the nozzle array inthe Y direction by whole multiples of the nozzle step from onecomplementary X motion to another may be added onto the shifts of partsof a nozzle step. A shifting algorithm that may be used may be similaror the same as that used between adjacent slices in, for example, U.S.Pat. No. 6,259,962, of the same assignees and which is incorporatedherein by reference.

In some cases printing a slice using more than two complementary Xprinting motions may cause a collision of the leveling device 157 withthe object This is because the tracks that are formed during an Xmovement from left to right be solidified before being leveled by theroller. In one embodiment this phenomenon may be prevented by includingtwo leveling devices, one on each side of the printing head array. In anadditional embodiment the apparatus may include only one curing lamp,located at a side of the leveling device (see FIG. 7C). In oneembodiment, when an even number of X printing motions may be required,the first movement may be a backward movement, for example, from rightto left. In all the subsequent forward movements, for example, left toright movements, except for the last left to right movement, materialmay be injected on tracks that are not touching their neighboringtracks. During the backward movements (except for the first backwardsmovement) material may be injected on tracks that touch theirneighboring tracks on each Y side. The tracks that touch neighboringtracks may protrude higher than the roller height in Z. Since these areonly the backward tracks, the roller can level up these tracks beforethey solidify, and collisions may be prevented.

An embodiment of this invention is illustrated in FIG. 7D. Profiles of 6tracks (in a case of 6 Y shifts, for example), corresponding to an i-thnozzle are shown in a Y-Z cross sectional view. As can be seen in FIG.7D, every time that a track is built higher than the roller height, thetrack may be printed during a backward movement, and therefore theleveler may easily level up the building material. The numbers in thefigure indicate the temporal order of track printing; B and F stand forForward and Backward

The droplet diameter d may set an upper limit on the possible resolutionr_(y) in Y direction that can be achieved while printing a slice, namelyr_(y)=1/d. According to an embodiment of the present invention, higherresolution may be provided in the Y direction. As can be seen withreference to FIG. 7E, when higher resolution in Y is required, acombination of two or more consecutive slices or layers may be used. Inthe first slice only part of the pixels set by the higher resolution maybe printed. An additional part of the pixels may be printed on thesecond slice, and so on.

For example if the required resolution is 3 times larger than 1/d, 3slices may be used in a way that the first slice prints, for example,1,4,7,10,13 . . . series of successive pixels, the second prints2,5,8,11,14, . . . and the third prints 3,6,9,12,15, . . . series. Ineach slice the content of the high-resolution pixel map may differ fromthe former slice according to the change of Z (the axis in the heightdirection). The grid of pixel locations, however, may preferably be keptconstant in respect to the X-Y start point. Because of the small slicethickness, the result of such printing may be very close to the resultof true high-resolution printing. This method may enable, for example,high resolution printing, but using a smaller data file than otherwisewould be required to obtain the same result.

It should be noted that the various methods and structures describedherein may be effected by a suitable 3-D printer and a controlling unitpossibly in conjunction with software and/or hardware elements, such asfor example, controller 105, printing apparatus 140 and the variousassociated components described in FIGS. 1, 2A and 3A, but may beeffected by other suitable 3-D printing software and/or apparatuseshaving other functionalities and structures.

The foregoing description of the embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. It should be appreciated by persons skilled in the art thatmany modifications, variations, substitutions, changes, and equivalentsare possible in light of the above teaching. It is, therefore, to beunderstood that the appended claims are intended to cover all suchmodifications and changes as fall within the true spirit of theinvention.

1. A three-dimensional object printing method, comprising: printing acarpet of building material on a printing tray prior to printing anobject, said carpet including one or more layers of modeling materialand being printed below and/or around the base of said object, saidcarpet serving to prevent infiltration of air and/or radiation betweenthe base of said object and said tray to prevent detachment of theobject from the tray.
 2. The method of claim 1, wherein said carpetprotrudes outside the boundaries of said object.
 3. The method of claim1, comprising covering said modeling material with one or more layers ofsupport material.
 4. The method of claim 1, wherein said layers ofsupport material keep said carpet flexible and adhesive in texture 5.The method of claim 1, comprising depositing additional modelingmaterial over said support material.
 6. The method of claim 1, whereinsaid carpet comprises layers of a combination of modeling material andsupport material.
 7. The method of claim 1, wherein the carpet comprisesone or more pillars of modeling material interspersed with supportmaterial.
 8. The method of claim 6, wherein the bottom layer includespixels of support material to ease detachment of the object from thetray after printing.
 9. A three-dimensional object printing methodcomprising: printing a construction of building material on a printingtray to form a base for an object to be printed; and dispensing buildingmaterial on top of said construction to form a three-dimensional object,wherein said construction is to adhere to said object and to saidprinting tray.
 10. The method of claim 9, wherein said constructioncomprises layers of modeling material and layers of support material.11. The method of claim 10, wherein said construction provides a barrierlayer between said object and said printing tray to prevent deformationdue to different thermal coefficients of the object and the tray. 12.The method of claim 10, wherein said construction provides a carpet forsaid object to prevent deformation due to lifting of the object and/orobject edges off the printing tray during printing.
 13. The method ofclaim 10, wherein the bottom layer includes pixels of support materialto ease detachment of the object from the tray after printing.
 14. Themethod of claim 10, wherein said construction comprises one or morepillars of modeling material interspersed with support material.